Everything was going well, when suddenly the screen was showing random pixels on the screen. I experienced the same issue few years ago when my favorite machine start showing the same pattern. It starts with few pixels, then you can barely understand what's going on in the desktop and finally screen becomes black or the computer restarts itself.
At that time the only solution was to throw my precious to the trash can (I am talking about the PC!). It was already old and almost impossible to find spare parts that will cost less than a new computer.
I was concerned that the faith of my wife's computer will be the same. We tried different things, like disabling some hardware in the BIOS and running RivaTuner to try to keep the GPU cool by "underclocking it".
As expected, nothing actually worked. The machine was behaving worst and worst.
After some research I found that it was possible to "bake" your video card in order to reconnect broken electrical connections. Several guides were available but the following video explains plain and clear how to do it.
The most difficult part is just to disassemble the computer. Fortunately DELL made public the document with these details [Dell 1520 Service Manual]. Of course it's not exactly straightforward, and you will need to unmount several parts to access the video card.
After you have the card at hand, you must separate it from the cooling system. I was a little bit afraid because the Cooling paste sticks very hard both parts, so you actually feel like if you break the video card, but don't worry, everything should be fine.
Then follow video directions: Bake the video card for 10 minutes at 200 Celsius. You will the effect because it will start smelling like "solder". Yummy!! It means your nvidia cookie is almost ready.
Assemble the whole guts and with some luck and magical dust your machine will come back to life.
I forgot to mention that this procedure worked 100% for me.
If you have some thoughts or questions, feel free to comment here.